Errors in number of function not implemented in dmd

output

$ dmd -c toot.d  
toot.d(6): Error: class toot.B interface function A.foo isn't implemented
toot.d(10): Error: class toot.C interface function A.foo isn't implemented
toot.d(10): Error: class toot.C interface function A.foo isn't implemented
toot.d(14): Error: class toot.D interface function A.foo isn't implemented
toot.d(10): Error: class toot.C interface function A.foo isn't implemented
toot.d(14): Error: class toot.D interface function A.foo isn't implemented

test.d

interface A
{
  void foo();
}

class B : A
{
}

class C : B
{
}

class D : C
{
}